relationship of crowding to disease states, therefore, may be a reflection of these other factors rather than the crowding per se.
How INCREASED SOCIAL INTERACTION LEADS TO DISEASE
Perhaps of greater importance than the inadequacy of the indicators or the presence of "contaminating" factors has been the failure of most investigators to identify explicitly the processes through which increased social interaction can lead to disease. The orthodox model which, implicitly at least, is espoused by the majority of authorities holds that crowding increases the risk of disease mainly through an increased opportunity for the spread of infection. Newer data and re-examination of older data are making this view increasingly untenable. It obviously cannot account for the increase in non-infectious disease which occurs under conditions of crowding; however, even for infectious diseases there is a growing body of opinion which indicates that such a view is at best only a partial explanation for any effects crowding may have. DuBos, the pioneer microbiologist, has perhaps stated this view most clearly:
The sciences concerned with microbial diseases have developed almost exclusively from the study of acute or semi-acute infectious processes caused by virulent microorganisms acquired through exposure to an exogenous source of infection. In contrast, the microbial diseases most common in our communities today arise from the activities of microorganisms that are ubiquitous in the environment, persist in the body without causing any obvious harm under ordinary circumstances, and exert pathological effects only when the infected person is under conditions of physiological stress. In such a type of microbial disease, the event of infection is of less importance than the hidden manifestations of the smouldering infectious process and than the physiological disturbances that convert latent infection into overt symptoms and pathology. (17)
According to DuBos, then, microbial disease is not necessarily acquired through exposure to a new microorganism. In a large number of cases disease occurs through factors which disturb the balance between the ubiquitous organisms and the host that is harboring them. It may well be that this balance may be disturbed under conditions of crowding, but this disturbance is then not a function of the physical crowding but of other processes. The studies reported above on upper respiratory infections in Marine recruits would tend to support this point of view. They suggest that a large proportion of the recruits are harboring organisms when they enter military training. Something about the military environment, particularly something about the environment of their own platoon or company, leads to the type of